Production of a semiconductor device involves a step of forming an electroconductive film on a surface of a semiconductor wafer (hereinafter also referred to as a wafer) to form a wiring layer by photolithography, etching or the like; a step of forming an interlaminar insulating film on the wiring layer; and the like; and an uneven surface made of an electroconductive material such as metal and an insulating material is formed on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring have been advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique in which while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with an abrasive in the form of slurry having abrasive grains dispersed therein (hereinafter, referred to as slurry).
As shown in FIG. 1, a polishing apparatus used generally in CMP is provided, for example, with a polishing platen 2 for supporting a polishing pad 1; a supporting stand (polishing head) 5 for supporting a polished material (wafer) 4; a backing material for uniformly pressurizing a wafer; and a mechanism of feeding an abrasive 3. The polishing pad 1 is fitted with the polishing platen 2, for example, by sticking with a double-sided tape. The polishing platen 2 and the supporting stand 5 are provided with rotating shafts 6 and 7, respectively, and are arranged such that the polishing pad 1 and the polished material 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pressing the polished material 4 against the polishing pad 1.
When such CMP is conducted, there is a problem of judging the planarity of wafer surface. That is, the point in time when desired surface properties or planar state are reached is required to be detected. With respect to the thickness of an oxide film, polishing speed and the like, the following has been conventionally conducted that a test wafer is periodically treated, the results are confirmed, and thereafter a wafer to be a product is subjected to a polishing treatment.
In this method, however, the treatment time of a test wafer and the cost for the treatment are wasteful, and the test wafer not subjected to processing at all in advance and a product wafer are different in polishing results due to a loading effect unique to CMP, and accurate prediction of processing results is difficult without actual processing of the product wafer.
Accordingly, there has been a need in recent years for a method capable of in situ detection of the point in time when desired surface properties and thickness are attained at the time of CMP processing, in order to solve the problem described above. In such detection, various methods are used. From the viewpoints of measurement accuracy and spatial resolution in non-contract measurement, optical detection means comes to be used mainly.
The optical detection means is specifically a method of detecting the end-point of polishing by irradiating a wafer via a polishing pad through a window (light-transmitting region) with light beam, and monitoring interference signal generated by reflection of the light beam.
As a method of detecting the end-point of polishing by such optical means, and a polishing pad used in the method, various methods and polishing pads have been proposed.
For example, there has been proposed a polishing pad comprising a polishing layer, and one or more transparent window members for optically measuring a polishing state, formed integrally with a part of the polishing layer, wherein each of the transparent window members is formed by laminating at least a soft transparent layer having a micro rubber A hardness of 60 degrees or less and a hard transparent layer having a micro rubber A hardness of 80 degrees or more, and also the soft transparent layer is located at an outermost layer of a polishing surface (Patent Document 1).
There has also been proposed a polishing pad comprising a polishing layer for polishing a material to be polished, and an underlying for supporting the polishing layer, wherein the polishing layer is provided with a first window member through which light is transmitted in a thickness direction, and the underlying layer is provided with a second window member through which light is transmitted in a thickness direction at the position corresponding to the first window member (Patent Document 2).
On the other hand, there has also been made a proposal for preventing a slurry from leaking from a polishing layer to a cushion layer.
For example, there has been proposed a polishing pad in which a transparent sheet is arranged between a pad lower layer and a pad upper layer so as to cover an opening of the pad lower layer and an opening of the pad upper layer (Patent Document 3).
There has also been proposed a polishing pad in which a transparent film is arranged between an upper layer pad and a lower layer pad (Patent Document 4).
As the transparent sheet (transparent film), a sheet (film) including an adhesive layer on both surfaces is used. However, in the case of providing such a sheet (film) between a polishing layer having a light-transmitting region, and a cushion layer, there has been a problem such as deterioration of accuracy of detection of optical end-point.